// Copyright (c) 1999-2004 Brian Wellington (bwelling@xbill.org)

package org.xbill.DNS;

/**
 * Constants and functions relating to flags in the DNS header.
 * 
 * @author Brian Wellington
 */

public final class Flags {

	private static Mnemonic flags = new Mnemonic("DNS Header Flag",
			Mnemonic.CASE_LOWER);

	/** query/response */
	public static final byte QR = 0;

	/** authoritative answer */
	public static final byte AA = 5;

	/** truncated */
	public static final byte TC = 6;

	/** recursion desired */
	public static final byte RD = 7;

	/** recursion available */
	public static final byte RA = 8;

	/** authenticated data */
	public static final byte AD = 10;

	/** (security) checking disabled */
	public static final byte CD = 11;

	/** dnssec ok (extended) */
	public static final int DO = ExtendedFlags.DO;

	static {
		flags.setMaximum(0xF);
		flags.setPrefix("FLAG");
		flags.setNumericAllowed(true);

		flags.add(QR, "qr");
		flags.add(AA, "aa");
		flags.add(TC, "tc");
		flags.add(RD, "rd");
		flags.add(RA, "ra");
		flags.add(AD, "ad");
		flags.add(CD, "cd");
	}

	private Flags() {
	}

	/** Converts a numeric Flag into a String */
	public static String string(int i) {
		return flags.getText(i);
	}

	/** Converts a String representation of an Flag into its numeric value */
	public static int value(String s) {
		return flags.getValue(s);
	}

	/**
	 * Indicates if a bit in the flags field is a flag or not. If it's part of
	 * the rcode or opcode, it's not.
	 */
	public static boolean isFlag(int index) {
		flags.check(index);
		if ((index >= 1 && index <= 4) || (index >= 12))
			return false;
		return true;
	}

}
